Referring to FIG. 1, a power supply system 2 is adapted to supplying power to an electronic circuit assembly 1 of an electronic device. The electronic circuit assembly 1 includes a functional circuit system 3 and the power supply system 2. The technical features of the functional circuit system 3 shown as a simple block in FIG. 1 depend on the type of the electronic device.
The power supply system 2 is usually a DC-to-DC transformer, such as a low-dropout (LDO), adapted to convert a relatively high voltage of 3.3V into 1.2V to be supplied to the functional circuit system 3.
The power supply system 2 has to supply the power required by the functional circuit system 3 in its entirety. In the situation where the operating maximum load current of the power supply system 2 is relatively high, the standby current of the power supply system 2 is also relatively high.
In the situation where the electronic circuit assembly 1 switches from an operation mode to a sleep mode or an idle mode, although the functional circuit system 3 is partially shut down, the power supply system 2 still has to stay in a standby state in order to wake up electronic circuit assembly 1 at any time. As mentioned above, the power supply system 2 with a high maximum load also has a high standby current; as a result, the electronic circuit assembly 1 in the sleep mode or idle mode still manifests overly high standby current consumption. The amplitude of the standby current of a conventional power supply system is not adjustable; as a result, the standby power consumption of a conventional power supply system cannot be reduced.